The present invention relates to a method of and a system for controlling an automatic transmission of a motor vehicle, and more particularly to a method of and a system for a gear shifting control by a hydraulically actuable coupling by a pressurized hydraulic fluid.
It is known in the prior art to control the pressure of the hydraulic fluid that serves to actuate the hydraulically actuable and frictionally engageable couplings of the automatic transmission in a manner dependent on various operating parameters of the motor vehicle in which the transmission is installed.
Various proposals have been made in improving riding comfort during a gear shifting. Japanese patent application first (unexamined) publications 62-93555 and 62-194940 disclose a gear shifting control wherein a stroke of a servo piston of a hydraulically actuable coupling to be engaged related to a new gear is detected and the pressure of the hydraulic fluid acting in the servo is controlled in accordance with the detected stroke position of the piston in order to alleviate the shift shock. This gear shifting control requires a position sensor for each of the couplings and thus poses a problem of finding a space for accommodating such position sensors.
U.S. Pat. No. 4,742,461 (Eschrich et al.) discloses another approach to improve riding comfort during gear shiftings. According to this known method, correction values for the pressure of the hydraulic fluid of the gear shifting control are determined by a comparison of reference values with average actual values and stored correction values. In the subsequent driving, the stored correction values are used to control the pressure of the hydraulic fluid medium to maintain a standard of comfort for all shift operations and new average actual values are used from time to time to modify the correction values.
An object of the present invention is to provide a gear shifting control which is improved such that after generation of a gear shifting command, an appropriate optimum timing at which the pressure for the hydraulic fluid begins to be controlled is accurately and reliably detected without relying on bulky position sensors.